1. Field of the Invention
The present invention generally relates to a developing apparatus for use in a laser printer or an electrophotographic copying machine and particularly relates to a single-component toner developing apparatus in which the density of a recorded image can be maintained stably.
2. Description of the Prior Art
Conventionally, in the developing apparatus of the type mentioned above using a single-component toner as a developer, a developing apparatus as shown in FIG. 9 has been generally used. Specifically, the developing apparatus includes toner box a for accommodating magnetic toner T a developer carrier b (hereinafter referred to as a "developing roll") in which a plurality of magnets are fixedly provided in a rotatable cylindrical sleeve so as to adhere the magnetic toner T onto the sleeve by magnetic force, and a blade c which is pressed against the developing roll b by pressure so as to form the toner T adhered on the developing roll b into a thin layer. With such a configuration, the thin-layered toner T is transferred onto an electrostatic latent image carrier d by the action of an electrostatic field formed between the developing roll b and the electrostatic latent image carrier d so that an electrostatic latent image on the electrostatic latent image carrier d is developed.
In such a conventional developing apparatus, however, some constituent members may deteriorate as time passes because of fatigue, toner dirt, or the like, and it is therefore necessary to perform maintenance, such as exchanging those members based on the time of use of the members. In view of simplifying maintenance in equipment such as an electrophotographic copying machine, a laser printer, or the like, it is therefore preferable to make the configuration of the developing apparatus so that the members that require maintenance (such as a developing roll, a blade, and the like) are separately arranged from the members that require no maintenance (such as the toner box).
Further, in view of minimizing the size of such equipment, it is necessary to effectively use limited space around the electrostatic latent image carrier. It is therefore preferable that the developing apparatus be of small size and simple configuration.
3. Description of the Related Art
Recently, therefore, there has been proposed a developing apparatus in which a developing roll and the like are made in the form of units so that the unit developing apparatus and the like can be removably attached to a toner box. Specifically, as shown in FIGS. 10 and 11, a toner agitation chamber (hereinafter referred to as "an agitation chamber") e is provided along the axis of a developing roll b, and a toner carry and supply member f is disposed in the agitation chamber e so as to be parallel to the developing roll b. In such a configuration, toner T is made to fall from a toner box a located at the upper portion of the developing apparatus into a toner carry-in path i projectingly provided on one end of the agitation chamber e. Thereafter, the toner T is dispersed, by the toner carry and supply member f, in the longitudinal direction of the agitation chamber e so as to be supplied onto the developing roll b. Further, in such a configuration, a toner level sensor g (FIG. 10) for detecting the quantity of toner supplied into the agitation chamber e is provided in the agitation chamber e, and a dispenser roller h provided in the toner box a is driven on the basis of a detection signal from the sensor g when the quantity of residual toner in the agitation chamber e becomes small so that the toner T is made to fall into the agitation chamber e to thereby prevent the toner from being exhausted in the developing apparatus.
Here, when toner is longitudinally, horizontally carried into the agitation chamber provided adjacently, to the developing roll as described above, to prevent uneven density from occurring in a developed recorded-image, it is important to accumulate the toner substantially evenly in the agitation chamber without allowing the toner to accumulate unevenly at a part in the longitudinal direction in the agitation chamber.
It is, however, difficult to make toner accumulate evenly in the longitudinal direction, and toner is apt to accumulate somewhat unevenly although it can be prevented from accumulating extremely unevenly if the shape of the toner carry and supply member or the like is improved.
In the developing apparatus of this kind, the quantity of residual toner in the agitation chamber is detected by the toner level sensor as described above. A problem may, however, occur so that the quantity of residual toner cannot be correctly detected dependently on the attachment position of the level sensor upon occurrence of uneven toner accumulation. That is, where the attachment position of the level sensor in the longitudinal direction of the agitation chamber coincides with the area in which the quantity of toner accumulation is large and, thus, the level sensor mistakes the quantity of partial residual toner for the quantity of whole residual toner, the toner cannot be supplemented from the toner box before the quantity of residual toner in the agitation chamber becomes extremely small.
A problem therefore occurs that, when a recorded image in which the image area is wide, such as a so-called solid image, or the like, (hereinafter referred to as a "high-area coverage image") is developed, toner may be partially exhausted in the agitation chamber so that the electrostatic latent image cannot be developed in an area corresponding to the position where toner has been exhausted and, therefore, image information will be lacking.
Further, recently, a laser printer or the like has been used as a digital information output unit in facsimile equipment, computers, or the like, and the foregoing problem is one of the important problems to be solved, in such a printer. Such a printer operates in an unmanned state at any time in accordance with image information supplied through a circuit such that lack of an image due to defective development is not permissible or compared to a copying machine or the like in which an image is formed in accordance with the operation of an operator.